irqchip: Silence sparse warning

drivers/irqchip/irqchip.c:27:13: warning: symbol 'irqchip_init'
was not declared. Should it be static?

Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Cc: trivial@kernel.org
Link: http://lkml.kernel.org/r/1393981281-25553-1-git-send-email-sboyd@codeaurora.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>